org.solovyev.android.list.ListViewScroller.java Source code

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Here is the source code for org.solovyev.android.list.ListViewScroller.java

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/*
 * Copyright 2013 serso aka se.solovyev
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.solovyev.android.list;

import android.app.ListActivity;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.widget.AbsListView;
import android.widget.ListView;
import org.solovyev.android.messenger.App;

import javax.annotation.Nonnull;
import java.util.concurrent.atomic.AtomicInteger;

public final class ListViewScroller implements AbsListView.OnScrollListener {

    private static final String TAG = App.newTag("ListScroller");

    /**
     * First visible item in list view. The value is changed due to list view scroll changes
     */
    @Nonnull
    private final AtomicInteger firstVisibleItem = new AtomicInteger(-1);

    @Nonnull
    private final ListViewScrollerListener listener;

    private ListViewScroller(@Nonnull ListViewScrollerListener listener) {
        this.listener = listener;
    }

    public static <A extends ListActivity & ListViewScrollerListener> void createAndAttach(@Nonnull A activity) {
        activity.getListView().setOnScrollListener(new ListViewScroller(activity));
    }

    public static <F extends ListFragment & ListViewScrollerListener> void createAndAttach(@Nonnull F fragment) {
        fragment.getListView().setOnScrollListener(new ListViewScroller(fragment));
    }

    public static void createAndAttach(@Nonnull ListView listView, @Nonnull ListViewScrollerListener listener) {
        listView.setOnScrollListener(new ListViewScroller(listener));
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        switch (scrollState) {
        case SCROLL_STATE_FLING:
            view.setScrollingCacheEnabled(false);
            break;
        case SCROLL_STATE_IDLE:
            view.setScrollingCacheEnabled(true);
            break;
        }
    }

    @Override
    public final void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        // we want to notify subclasses about several events
        // 1. onTopReached
        // 2. onBottomReached
        // 3. onItemReachedFromTop
        // 4. onItemReachedFromBottom

        if (this.firstVisibleItem.get() >= 0 && visibleItemCount > 0) {
            boolean scrollUp = false;
            boolean scrollDown = false;
            if (firstVisibleItem < this.firstVisibleItem.get()) {
                scrollUp = true;
            }
            if (firstVisibleItem > this.firstVisibleItem.get()) {
                scrollDown = true;
            }

            final int lastVisibleItem = firstVisibleItem + visibleItemCount;

            switch (view.getId()) {
            case android.R.id.list:
                if (scrollUp && firstVisibleItem == 0) {
                    Log.d(TAG, "Top reached");
                    // reach top
                    listener.onTopReached();
                } else {
                    if (scrollDown && lastVisibleItem == totalItemCount) {
                        // reach bottom
                        Log.d(TAG, "Bottom reached");
                        listener.onBottomReached();
                    }
                }

                if (scrollDown) {
                    listener.onItemReachedFromTop(lastVisibleItem, totalItemCount);
                }

                if (scrollUp) {
                    listener.onItemReachedFromBottom(lastVisibleItem, totalItemCount);
                }

                break;
            }
        }

        this.firstVisibleItem.set(firstVisibleItem);
    }
}